**2. Uses and trends for sugarcane bagasse valorization**

Bagasse consists of fibers (48%), water (50%) and soluble solids such as sugars (2%) [4]. Bagasse is an important lignocellulosic material containing cellulose 42%, hemicellulose 28%, lignin 20%, 4.6% of other polysaccharides, 3% of saccharose and 2.4% of ash, on a dry weight basis [5]. Lignocellulosic biomass has been used to produce second-generation ethanol and other by-products such as xylitol by sugarcane agroindustries. Various energy products can be generated from the lignocellulosic composition using biochemical and thermochemical processes. For example, sugarcane bagasse is an economically viable and promising raw material for bioethanol and biomethane production [6, 7]. Bagasse is typically used to produce heat and electricity in sugar mills (cogeneration), but can also be used for paper making, as cattle feed and for manufacturing of disposable food containers. Currently, bagasse is mainly used as a fuel in the sugarcane industry to satisfy its own energy requirements. However, there is a surplus of this bagasse which could be diverted to other uses such as the production of single cell protein, ethanol, enzymes and food additives such as vanillin [8] and xylitol [9, 10]. The sugarcane bagasse surplus is used in more than 40 different applications, including pulp and paper, boards, animal feed, and furfural [11, 12]. **Figure 1** shows some of the various uses of the sugarcane bagasse.

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The extraction of sugar from this crop generates several residues that are often disposed improperly especially where sugar mills use basic process technology. The huge quantities of solid waste are often destroyed or burned inefficiently causing environmental pollution [1]. Sugarcane solid residues include bagasse and filter cake. Bagasse is the solid residue resulting after the juice extraction from the sugarcane stalks and contains the fibrous lignocellulosic material of the stalks. The precipitate in the form of sludge slurry after filtration of the sugarcane juice is the filter cake. Every 1000 tons of processed sugarcane generates about 270 tons of bagasse and 34 tons of cake [2]. Approximately, 1.81 billion tons of sugarcane were produced worldwide in 2015, and this is expected to reach more than 2.21 billion tons by 2024 [3]. Based on these values, the world's potential generation of sugarcane bagasse will reach 0.6 billion

The expected increase in bagasse availability is driven by the increasing demand for sugar, and sugarcane is the most important source of sugar in the world. However, sugar industries are one of the most polluting ones in view of the generated solid wastes, wastewater, and gaseous emissions of carbon monoxide, volatile organic compounds, and also greenhouse gases during crop cultivation phase [1]. Transforming all by-products obtained from sugar mills (bagasse, filter mud, fly ash and molasses) into value-added products will minimize the pollution to a large extent. Treating sugar industry effluent for reuse in agriculture and other applications is another strategy to reduce the environmental impacts. In summary, sugar industry wastes should be seen as economic resources that can be converted into valuable products in progressing toward resource recovery as a sustainable solution that could generate social welfare and economic development from the sugarcane industry and its residues. In this chapter, the use of sugarcane bagasse as a raw material for energy generation versus bioethanol production is discussed.

Bagasse consists of fibers (48%), water (50%) and soluble solids such as sugars (2%) [4]. Bagasse is an important lignocellulosic material containing cellulose 42%, hemicellulose 28%, lignin 20%, 4.6% of other polysaccharides, 3% of saccharose and 2.4% of ash, on a dry weight basis [5]. Lignocellulosic biomass has been used to produce second-generation ethanol and other by-products such as xylitol by sugarcane agroindustries. Various energy products can be generated from the lignocellulosic composition using biochemical and thermochemical processes. For example, sugarcane bagasse is an economically viable and promising raw material for bioethanol and biomethane production [6, 7]. Bagasse is typically used to produce heat and electricity in sugar mills (cogeneration), but can also be used for paper making, as cattle feed and for manufacturing of disposable food containers. Currently, bagasse is mainly used as a fuel in the sugarcane industry to satisfy its own energy requirements. However, there is a surplus of this bagasse which could be diverted to other uses such as the production of single cell protein, ethanol, enzymes and food additives such as vanillin [8] and xylitol [9, 10]. The sugarcane bagasse surplus is used in more than 40 different applications, including pulp and paper, boards, animal feed, and furfural [11, 12]. **Figure 1** shows some of the various uses of

tons, which could be valorized into bioenergy, biofuels, and other products.

**2. Uses and trends for sugarcane bagasse valorization**

the sugarcane bagasse.

72 Sugarcane - Technology and Research

**Figure 1.** Uses of sugarcane bagasse in energy, biochemical, food and feed, and materials applications.

Bagasse is used as a more sustainable source of diverse paper products including toilet, tissue, corrugating medium, news print and writing paper [13–15]. Poopak and Reza described the process of paper making which starts by separating bagasse fibers from the pith by mixing it with water and using a dewatering unit [15]. Fibers are then cooked approximately 10–15 min in a steam boiler, where a black liquor or pulp remains in container. This pulp is washed to remove the color and then sand and undesired fibers are removed by screening and cleaning. Afterwards, pulp thickening reduces the water to about 12%, and it is further processed for whitening the pulp by using chlorine gas and NaOH. This pulp is then ready to supply to a paper mill where the pulp will go through several processes to create paper products. The use of sugarcane bagasse as a renewable raw material can be a sustainable option to reduce deforestation and impacts of the pulp and paper industry.

Charcoal from sugarcane bagasse is another possible source of heating and cogeneration of energy, and can be produced according to the following simplified process [1]. Bagasse is collected and passed through a pyrolysis step where it gets fully carbonized. The resulting powder is mixed with a binding material such as starch and then boiled with water so that it can be extruded to form briquettes or other desirable shapes of charcoal to be sold as a solid fuel.

Recent trends in the use of sugarcane bagasse include new and improved applications in the areas of materials. For example, the bagasse has been used as an excellent soil conditioner to improve sugarcane plant productivity and health [16]. Sugarcane bagasse can also be used for products that improve the durability and mechanical properties of construction materials and as a binder [17]. The bagasse fibers can also be conditioned to be used in the textile industry [18], and as an effective adsorbent material to remove toxic metals and dyes from wastewater [19, 20]. More recently, sugarcane bagasse has been used as a raw material to produce carbon quantum dots which can be used as biosensors in light-emitting diodes and even in drug delivery [21]. This chapter concerns the two most common applications of energy and bioethanol production from sugarcane bagasse, which are described in the following sections.

extraction steam turbine (CEST) system in **Figure 2b** is more complex and more expensive than BPST, but achieves higher efficiencies and higher electricity surplus, have more flexibility and can operate the whole year. In this system, the high-pressure steam can be expanded at different lower pressure levels and extract the steam required for process or produce further electricity. Typically, the high-pressure steam is at 65–100 bar and can be expanded at 22 and

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The use of sugarcane bagasse for bioethanol production has been extensively researched in recent years [23, 24]. The processing of sugarcane starts with the cleaning of sugarcane and extraction of sugars: juice treatment, concentration and sterilization [25]. Sugar extraction is carried out using mills to produce a sugarcane juice which follows a series of treatment, clarification and dewatering until the crystallization and centrifugation of sugar crystals. The production of ethanol from the juice, molasses or bagasse includes additional processing units of

Ethanol can be prepared by the fermentation of molasses which contain 60% of fermentable sugars as described in [1]. Molasses is first diluted with water in 1:5 (molasses/water) ratio by volume. If molasses lack sufficient amount of nitrogen, it is fortified with ammonium sulfate to provide adequate supply of nitrogen to yeasts. Fortified solution of molasses is then acidified with a small quantity of sulfuric acid. The addition of acid favors the growth of yeasts and hinders the growth of unwanted bacteria. The resulting solution is then transferred to a large tank, and yeast is added to it at 30°C and left to ferment for 2–3 days. During this period, sucrase and zymase present in yeasts convert the sugars in molasses into ethanol according to

C<sup>12</sup> H<sup>22</sup> O11 + H<sup>2</sup> O 2C6 H<sup>12</sup> O<sup>6</sup> (1)

C<sup>6</sup> H<sup>12</sup> O<sup>6</sup> 2C2 H<sup>5</sup> OH + 2CO2 (2)

The alcohol concentration in the fermentation broth is only 15–18%. The broth is sent to a distillation system to obtain 92% pure alcohol, also known as rectified spirit or commercial alcohol. A further purification step by molecular sieves or pervaporation is needed to produce

An additional pretreatment step is needed in the production of bioethanol from bagasse. Pretreatment of the sugarcane bagasse is important because it helps to separate lignin and hemicellulose from cellulose, reduce cellulose crystallinity and increase the porosity of bagasse, thus improving cellulose hydrolysis [27]. Lignocelluloses are made up of three main polymer types: lignin encasing cellulose in cell walls provides rigidity of cell walls, hemicelluloses cover the cellulose and strengthen cell walls by interaction between lignin and cellulose, while encased cellulose microfibrils gives tensile strength to cell walls [28]. Celluloses

**4. Valorization of sugarcane bagasse for bioethanol production**

2.5 bar with a final condensing stage at 0.135 bar.

fermentation, that is, distillation and dehydration.

the following simplified chemical reactions [26]:

anhydrous bioethanol for blending with gasoline.
